Semiconductor components typically contain a large number of devices in addition to semiconductor chips. These devices include passive devices (e.g., resistors, coils, capacitors and diodes).
For example, U.S. Pat. No. 6,313,521 (Baba) discloses a component in which a semiconductor chip and passive components are arranged on a substrate. The semiconductor chip is designed as a flip chip and provided with an underfilling material. An adhesion promoter which conducts heat and electric current is applied to the exposed upper side of the semiconductor chip and joins the semiconductor chip to a heat sink. If, in the case of this arrangement, an excessive quantity of adhesion promoter is applied to the upper side of the semiconductor chip during mounting, there is the risk that the conductive adhesion promoter will produce a contact with the passive components and short-circuit the latter. In order to avoid this, it is proposed to embed the passive components with their lateral sides and their rear sides in the underfilling compound of the flip chip.
In order to increase the reliability of the soldered joint between passive device and substrate, it is also known to provide the passive devices themselves, if they are surface mountable, with an underfilling material, which is introduced into an interspace between the substrate and the underside of the device, in a manner similar to flip chips. This results in a reduction in the risk of damage to the soldered contacts in the event of alternating thermal loading because of different thermal expansion coefficients of device and substrate, which can lead to cracks or similar damage to the soldered joint. Typically, the underfilling material used is a material which, by way of capillary action, can be introduced into the interspace without pressure and forms a meniscus at the lateral sides of the device.
However, in the case of such devices embedded with the underside and the lateral sides in the underfilling material, it is possible for problems with what is known as the “solder pumping” effect to occur during subsequent soldering processes during the board mounting by the user. In this case, the underfilling material expands during the reflow and forces the liquid solder out of its cavity. In this way, the liquid solder can, for example, be “pumped” to the upper side of the device.